Activation manner and sensor less motor null of sensor less

摘要

PURPOSE:To start surely and permit automated manufacturing by a method wherein predetermined magnetic field is supplied to the core of a detecting coil upon detecting a counter electromotive voltage generated in a driving coil by the rotation of a rotor after supplying predetermined starting current to the driving coil. CONSTITUTION:A biasing magnet 4 is magnetized so as to have four poles in the circumferential direction thereof. A predetermined bias magnetic field is impressed on the core by these poles. The biasing magnet 4 impresses biasing flux on respective cores while an external magnetic field is impressed so as to be superposed on the biasing flux. When the bias flux density of +B1 is impressed on the core, for example, the saturating degree of the flux density B is different between a case, when the magnetic poles of a rotor are proximated and the change + B of the flux density is generated, and another case, when the change - B of flux density is generated. Accordingly, induced voltages, proportional to the changing widths of respective flux densities, are generated whereby identification whether the proximated magnetic pole is N-pole or S-pole can be effected by detecting the difference of the change of the generated flux.